1. Technical field
The present invention relates to a differential refractive index detector and a liquid chromatograph equipped with the same.
More specifically, the present invention relates to a differential refractive index detector which can automatically perform the processing from the eluent purge operation of reference cell at the start of operation until the stability confirming operation by judging whether or not the detector was stabilized in an analysis capable condition, thereby enabling more efficient analysis work, and also relates to a liquid chromatograph equipped with the detector.
2. Related Art
FIG. 5 is a block diagram showing the outline of a conventional differential refractive index detector for a liquid chromatograph. As shown in FIG. 5, a conventional differential refractive index detector comprises two cells 11 and 12 consisting of a reference cell 11 for filling with or passage of a reference solution and a sample cell 12 through which a solution containing a sample is passed. These cells 11 and 12 are disposed such that their slant faces oppose each other. The sample cell 12 is connected by an eluent inlet line 14 for introducing an eluent eluted from a separation column 13 and by a sample cell outlet line 15. The reference cell 11 is connected by a reference cell inlet line 16 communicating with the sample cell outlet line 15 and by a reference cell outlet line 17.
At the connection between the reference cell outlet line 17 and a line 18 externally extended from the connection of the sample outlet line 15 with the reference cell inlet line 16, a three-way solenoid valve 19 is provided. To this three-way solenoid valve 19, an eluent outlet line 20 for discharging the eluent outside is connected. By intermittently switching over the three-way solenoid valve 19 on demand, the eluent which was flowed out from the sample cell 12 can be intermittently allowed to flow into the reference cell 11.
On one side with respect to the reference cell 11 and the sample cell 12, a light source 21 for irradiating a measuring beam is provided, and on the other side, a reflector 22 for reflecting the measuring beam transmitted through these cells 11 and 12 is provided. Furthermore, in the vicinity of the light source 21, a photoreceptor device for detecting the displacement of the measuring beam accompanying the difference in the refractive index of the eluent in the two cells 11 and 12 is provided.
The light source 21, the photoreceptor device 23 and the three-way solenoid valve 19 converge at a signal processing part 24. The signal processing part 24 has a function of outputting the difference in refractive index of the eluent into two cells 11 and 12 as an electric signal based on a signal sent from the photoreceptor device 23 and at the same time, controlling the driving of three-way solenoid valve 19 and the driving of light source 21 based on an operation signal sent from the outside.
In the conventional differential refractive index detector, electric power is charged and then start-up is initiated by an input unit not shown, as a result, the three-way solenoid valve 19 is actuated through the signal processing part 24 to bring a state such that the piping 18 is closed and the reference cell outlet line 17 communicates with the eluent outlet line 20.
Subsequently, the following operations are performed in sequence.
(1) Initial Solution Purge Operation
This is an operation of purging the inside of the reference cell 11 with an eluent at the start of operation of the differential refractive index detector.
(2) Stabilizing Solution Purge Operation
This is an operation of confirming whether factors other than the change of refractive index are in a stabilized condition by continuously passing an eluent which has flowed out from the sample cell 12, through the reference cell 11.
(3) Stability Confirming Operation
This is an operation of confirming whether or not the differential refractive index detector has stabilized in an analysis capable condition while keeping the flow passage in an analyzable condition by stopping the flow of eluent into the reference cell 11.
Through these operations, the differential refractive index detector can be stabilized in an analysis capable condition.
In the case where a conventional differential refractive index detector is used as a liquid chromatograph detector, the change in the refractive index of the eluent causes a serious problem. The refractive index of the eluent changes not only with the elution of a sample but also by the staining of eluent itself, the dissolved gas concentration, the temperature and the like. Accordingly, in order to stabilize the differential refractive index detector at the start of operation, unlike an ultraviolet absorbance detector which is a general liquid chromatograph detector, an initial solution purge operation of purging the referential cell 1 with a solution at the start of operation and subsequently stabilizing the solution purge operation, and stability confirming operation of monitoring the output signal (chromatogram) over a relatively long period of time until a stable condition is reached are necessary. Thus, much labor and a long period of time are disadvantageously required.
Furthermore, the judgement that the differential refractive index detector has reached a stable condition is made by intuition in many cases and greatly depends on the experience and skill of the judging person. This naturally brings about great personal errors in the judgement of stable condition. Depending on the case, the condition may be excessively stable or may be deficient in stability. Thus, this intuitive judgement is disadvantageous in that an efficient operation cannot be attained.